The last mitzvah in our parasha is the commandment of tzitzis. Eight strings adorn each of the four corners of a garment. These eight strings, comprised of blue and white, must be wound and knotted partially (the g'dil) with the rest of the strings hanging loose (the anaf).
R. Meir Simcha of Dvinsk in his Meshech Chachma suggests an insightful reason for the mitzvah of tzizis and many of its details. Here we present his inspiring words with some additional elaboration. Hashem Yisbarach created a world in which His Divinity is hidden. In the upper worlds, Hashem's majesty is directly manifest. The heavenly angels are immediately aware of the reality of the Divine Existence and that It alone is true reality. Their kabbalas 'ol malchus shamayim is reflective of a given reality: "baruch sheim k'vod malchulso l'olam va'ed - may the name of the glory of His majesty be blessed forever." There the majesty is already apparent; they need no convincing. Mankind, living in the lower world, one in which G-d's presence is not apparent, needs to reveal G-d within the world. They need to convince themselves that the world is just a mask hiding the inner dimension of G-dliness within. Their kabbalas 'ol malchus shamayim is "Sh'ma Yisrael, Hashem Elokeinu, Hashem Echad." To paraphrase, "Listen to me Reb Yid, the world might appear to follow a natural order but within this order G-d 's Presence is always there; He is always ready to be discovered and the world was built for this purpose. Make sure not to get caught up in this concealment and forget the Creator c"v!"
The initial creation of the world is therefore described as a garment. The verse many recite before donning the talis states: "[Hashem] wraps light (the first creation) like a garment" (Tehillim 104:2). Just as a garment hides the person, so too, the world hides, so to speak, its Creator. By creating such a world, an incomplete world, where G-d's presence is not immediately apparent, Hashem allowed Man to actualize his latent potential in discovering Him and utilizing all of the physical aspects of the world to serve his Creator. In doing so, he partners with G-d to complete the world. In the famous analogy, R' Akiva teaches the Roman general, Turnurufus, that just as bread is tastier than wheat having been processed by Man, so too do we do mila indicating that the human being must perfect himself and the world. This was directly in contrast with the Roman notion that circumcision is needless mutilation and Man is already perfect. This is not so - G-d created Man in an imperfect state commanding and directing that he perfect himself and the world as well by revealing the Creator.
Tzitzis, too, highlights this partnership. On the garment - perhaps we can add the four cornered one symbolizing the "four corners of the world" - we place strings that are seemingly incomplete and not woven together with the rest of the garment. This represents the arena for Man to elevate himself by completing the creation, recognizing G-d, and utilizing the world to connect to Him. But even within this sphere of activity, G-d's assistance is ever present. Even within the unfinished strings, they are partially wound with techeiles, symbolizing G-d's presence and assistance (see Sota 17a). Man is not alone in his endeavor to reveal his Creator's presence; he is constantly assisted. Hashem is "maichin mitz'adei gever - He prepares the steps of Man" and constantly assists Him (see Kiddushin 30b).
In a somewhat different vein, I once heard from Rav Aharon Lichtenstein shlita, (any error in presentation is my own) that Jews share a common humanity and human values with the rest of the nations of the world. But in order to demonstrate that these common values, this common humanism, also must be imprinted with specifically Jewish, Torah values we tie the tzitzis onto our garments which distinguish us from the animal kingdom - only humans wear clothing. The Jewish people indicate that their human value system, symbolized by their clothing, is a uniquely Jewish one.
Perhaps according to both of these ideas we can understand an additional reason (see Berachos 12b) why the parsha of tzizis is included in the recital of the shema, symbolizing as it does both the entire purpose of creation and the unique Jewish attitude toward human values.